Having an intermittent MAF code 33. Clear codes and all is well for a day or two.

Where is this expensive piece, burn off module? Need to check voltage at the burnoff connector harness but can't find it.

Have looked in and around the ECM to no avail. Found a couple of modules including the Theft Deterent and a small module that my local dealership says is discontiued; they can't tell me what is it is.

I've looked for burnoff connector wire colors identified in the service manual, but just can't find them.

Upside down looking at the ECM, which direction?

Thanks for any help.

Update for you guys who may run into an intermittent code 33 on a 1985 Corvette. The following is a list of things I did wrong and right using the GM Service Manual.

1. The code 33 was intermittent. Upon clearing the code by disconnecting the battery ground, sometimes I would find the correct voltages at the maf connector and sometimes I wouldn't. I would occassionally find no voltage, 12v, on terminal E of the maf connector. This led me to the burn off module which supplies the 12 volts. Other times all voltage readings were correct and the shop manual said "replace the maf".

2. Error #1, I replaced the maf with a brand new GM/Bosch unit and continued to get an intermittent code 33. I should have known that I had something going on besides a bad maf with the code and voltages being intermittent.

3. I then went in pursuit of the burn off module, harness connection, and wiring. Performed continuity checks per the shop manual and all was ok. Had to teach myself how to do this with some help from a friend.

4. Next, started looking for the burn off module because I "felt" it was the culprit. Thanks to LD85 I was able to find the thing mounted on a bracket inside the crash pad/bread basket. As LD85 described you have to remove the dash pad and bread box which is a journey into hell for us non techs. I'm an accountant by trade who plays Mr. Fixit so I'm sure a tech would have had the job done in 1/4 of the time it took me.

5. The burn off module is sealed inside an aluminum case. I wanted to see this $950 (dealership retail price) circuit board so I removed it from the case to find circuit board with capacitors, resisters, couple of chips, and the relay. Nothing really exotic. Could not find anyone who repairs the thing via google searches, local electronic repair shops.

6. After removing the circuit board from the case, I decided for some reason to reconnect the board, without the case, to the harness. Left the exposed circuit board connected to the wiring harness laying on the carpet floor. Made probably 50 engine starts and drove the car 50 miles without a fault.

7. In the course of events I made a post asking if anyone had a working unit for sale and LD85 responded giving me a great/great/great price on a unit he said was working when he pulled it out of the car.

8. I received the unit from LD85, plugged it in leaving the unit laying on the carpet floor. Worked great, many starts, 50 miles or so. Now my mindset is put the sh.. back together. Started with mounting LD85's unit on the bracket. I stopped there, divine intervention. After mounting the unit on the bracket, I went out for a test drive and guess what; code 33.

9. Today, I removed the unit LD85 sent from the mounting bracket, placed on the carpet, still inside its case, performed 10 engine starts with no problem. I then drove the car 35 miles, in traffic, interstate, known rough/bumpy roads with no problems. Shut the engine down and have performed 5 starts with no problems.

Sorry to be long winded. I'm going to drive the car for a week in this condition; burn off module in the case laying on the carpet floor. If no, problems, I will re-locate the burn off module, wrap it in rubber.

Just wanted to share this with 1985 owners who might someday run into an intermittent code 33. Why it likes the carpet and not the mounting bracket, I don't know. Must have some some wiring grimlen or a vibration issue. If all goes well the next couple of days, I will hide it from the grimlem!

 

Its behind the Crash Pad on the passenger side, bolted to a small bracket way up in there! Sorry!

 

it is behind the breadbox on the passenger side. A check for operation is to , take off the MAF hose so you can look into the MAF sensor, have the ign switch on engine off, ground the ALDL term E, shut the ign off and very quickly look into the MAF sensor to see if the wire glows, if so its good. You may want a helper to view the MAF unit as these events happen quickly.

 

Code 33 isn't usually, not to say it couldn't be, a burn off problem.

Code 33 is usually sent when the ECM doesn't sense the MAF itself.

On a properly functioning system or in the case of a code 34, low volts to the MAF, if you disconnect the wiring harness on the MAF you will get a code 33.

Do you have a scanner?

I bought one (auto Xray) and it has saved me hundreds in not replacing parts that weren't bad and countless hours of frustration

If you like, I caan fax you the Helms diagnostics for code 33 and 34

May take a couple of days, e mail me a fax number

Jack

 

Thanks for the input from you guys. I have the GM service manual and have gone through all the diagnostic tests. Sometimes I have 12 volts at the MAF connector on terminal E and sometimes I don't. Also get good readings sometimes and not on MAF connetor for terminals A and E and B and E. These tests led to the MAF malfunctioning.

I replaced the MAF out of frustration but still get three good starts and the car runs fine; and then code 33 on the 4th start.

jackdaroofer, I don't have a scanner but have access to one. I'll try that route.

Puzzle. Why good starts and runs and then code 33? Could the ECM be going bad, not recognizing info from the MAF? Could it be vibration or heat. I can clear the code by disconnecting the battery and she is good to go. Drove it 10 miles this evening with no code. Cranked it a couple of times after the drive, and then code 33.

What does the burn off module look like? I can't find a module with the wiring colors specified in the GM shop manual.
If I can find it, I'll check to see if voltage is present at that source the next time the code is set.

I'm an accountant trying to be a tech!

Thanks guys.

 

Not real sure about its location on the Vette BUT on the F bodys it was piggybacked on the ECM. It is silver (raw alumnium) about 3.5" wide X 6.5" long X 1.5" thick and says Bosch on it.
The module is supposed to supply MAF power and burn off function.
GM wants $780 for one..don't go there.
If you do all of your troubleshooting and it points to the module...let me know I have 1 or 2 spares laying around, I can't vouch for their functionality but you are welcome to try one for the cost of shipping.

 

Thanks for the generous offer Morley. I need to finish trouble shooting before I do anything else.

My first goal is to find the module, and I will find it if I have to take the entire dash out! I performed testing per the shop manual last night and had to stop because I could'nt test the voltage output from the burn off module at the F terminal of the module.

Thanks!

 

LD85,

I've been looking for the burn off module,not very hard, and overlooked your post as to location.

Do you know the procedures for getting to the burn off module? I have the GM shop manual but it just says remove module and then re-install module.

Thanks for any help you can give me.

 

The easiest way to it take your top dash pad off then you can reach down behind the pad and grab it, The unit is held onto the back of the crash pad bracket by sheet metal screws.

The dash is held on buy two screws in the top center by the defroster vent, then @ 6 or so under the dash lip

 

Thanks for the tip. I'll give it a try.

 

LD85, found and removed the module using your tip. What a place to mount one this module!

I can't believe no one services these simple looking devices. Guess Bosch intended to keep design/specs private so they could sell them for 2-3 times more than the ecm costs.

Morley, is your offer still good?

 

Cool, if you cant find one I can sell you mine cheap , but I cut the plug off of the end of the wires. $20 shipped

 

LD,

Was it working when you removed it? If I understand where you cut it, I could use my connector right?

Thanks.

 

Yes it was working and yes you could use your own plug.

 

Thanks LD85.

Give me your address and I will mail a money order to you tomorrow.

Please send the module to my work address:

More Performance, Inc.
Attention: Skip Norris
2919 Interstate Street
Charlotte, NC 28208
Tele# 704-393-8241

Thanks for your help with problem.

 

I mailed it today, via USPS Priority you can email me at ldickey10@comcast.net

 

I had the exact same code issue on my 87. I looked for the burn off module under to dash on passenger side. (What a pain) I finally found the module (2 of them) located directly behind the battery mounted to the fire wall. Replaced both of them. Cleared the code, and Its been fine since then.